Abstract: We have performed O self-diffusion experiments in synthetic diopside single crystals along the b-axis at temperatures ranging from 1473–1643 K, under controlled O partial pressure (10⁻¹¹–10⁻² atm). The ¹⁸O tracer diffusion was imposed by solid/gas exchange between ¹⁶O in diopside and ¹⁸O₂-enriched argon-hydrogen-H₂O gas mixture. Diffusion profiles of ¹⁸O were measured by Nuclear Reaction Analysis ¹⁸O (p,α) ¹⁵N. The diffusion coefficients are described by D=D0exp(−ERT), with log D₀(m²/s)=−9.2 ± 1.0 and E 310 ± 30 kJ/mol.

Our results are in agreement with Ryerson and McKeegan's (1994) data and Farver's (1989) data along a direction perpendicular to the c direction. Experiments performed in a wide pO₂ range show that D is independent of pO₂.

We observe no change in the diffusion regime up to 1643 K (i.e. 22 K prior to melting temperature). This result differs from the diffusion study of Ca in diopside by Dimanov and Ingrin (1995), where a strong enhancement of Ca mobility, attributed to an excess disorder in the Ca-sublattice, was observed above 1523 K. We conclude that O diffusion in diopside is not affected by this premelting phenomenon.